1. Field of the Invention
The present invention relates to an actuator control apparatus for an internal combustion engine such as an exhaust gas recirculation control apparatus.
2. Description of the Related Art
In an exhaust gas recirculation control apparatus used in an internal combustion engine, an EGR valve is provided in an exhaust gas recirculation passage for appropriately adjusting the EGR (exhaust gas recirculation) ratio in accordance with a driving state of the internal combustion engine (Japanese Patent Applications Laid-open No. HEI 1-295666 and No. HEI 2-267357). The opening degree of this EGR valve is controlled by the adjusted vacuum pressure supplied from an electronic vacuum regulating valve. In this case, the opening degree of the EGR valve is determined by a balance of vacuum pressure from the electronic vacuum regulating valve and back pressure in the exhaust gas recirculation passage.
However, if the opening degree of the EGR valve is too small, chattering is generated in the EGR valve due to variations in the back pressure, and noise and variation in the EGR ratio may result.
In order to prevent this, as shown in FIG. 9, when the opening degree of the EGR valve is adjusted in accordance with the driving state of the internal combustion engine, an electric current value capable of achieving an opening degree at which no chattering is generated in the EGR valve in entire driving region of the internal combustion engine is preliminarily set as a current value of the lower limit MIN such that only currents greater than this current value of the lower limit MIN are supplied to the EGR valve, and, when a current value lower than the current value of the lower limit MIN is required, the current is set to "0", and no current is supplied.
If the current value of the lower limit MIN at which no chattering is generated in the entire driving region of the internal combustion engine is set, and the opening degree of the EGR valve is uniformly controlled in this manner, it is possible to reduce the chattering of the EGR valve. However, according to this control a driving region exists in which, even when the opening degree of the EGR valve is controlled by a current value smaller than the current value of the lower limit MIN, the opening degree can be controlled without generating chattering in the EGR valve.
In this manner, even in a driving region in which the current value can be reduced to a value smaller than the current value of the lower limit MIN, current values smaller than the current value of the lower limit MIN cannot be obtained. Therefore, although it is preferable for fuel efficiency, emission control and the like to conduct EGR, EGR execution may not occur.